Literature review: Impact of Chilean needle grass ... - Weeds Australia

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correlated with significant reduction in native plants, but high native cover had no such relationship (Morgan 1998d). However native plant species richness per se does not appear to inhibit exotic plant invasion in these grasslands (Morgan 1998d). Damage to the cryptogam crust appears to be one factor that facilitates invasion (Scarlett 1994), presumably because it enables more rapid seed burial and therefore decreases exposure of exotic seeds to fire and predators (Morgan 1998d), but possibly also because of the nutrient fluxes that result. At the landscape scale, high levels of fragmentation by roads and proximity to agricultural land and urban areas makes native grassland more invasible (Williams 2007).These factors are important drivers of propagule pressure, that increase movement of seeds from established weed infestations into the surrounding landscape (Melbourne et al. 2007). Similarly, the factors with the most influence on the extinction of native plants from grassland remnants in the Victorian basalt plains have been found to be the road density of the surrounding landscape, and long intervals between fires, which are general indicators of habitat degradation (Williams et al. 2006), and probably represent good indicator measures of the invasibility for such grasslands. Apart from factors that affect colonisation pressure, the extent and nature of resource fluctuation is probably the main determinant of what species invade (Morgan 1998d). In effect, exogenous disturbance is “a special case” of environmental heterogenity (Melbourne et al. 2007 p. 78) – the greater the severity and range of such disturbances, the greater the invasibility of the area. Impact Impact has been defined as the effect that an invader has on the invaded system once established (Melbourne et al. 2007), however this approach ignores effects associated with the establishment phase, and longer term effects post-establishment. Immediate impacts during the establishment phase might be substantial (e.g. lethal toxicity to animals) and long-term effects might include changes to the abiotic environment (e.g. changes to soil pH). The approach also distances any analysis from whatever management is targetted at the invader, and ignores effects that persist after its eradication or removal (Mgobozi et al. 2008). Furthermore such an approach glosses over the complexities of evolutionary change that are likely to occur in the invader and the invaded system as they interact (Whitney and Gabler 2008). Since very few plant invaders are ever eradicated, ultimately both the invader and the invaded system adapt to accomodate each other, and since there is more adaptive potential in the community that the single invader, the impact will eventually decay, or, if these adaptive changes are themselves considered to be impacts, may continue to slowly increase (Fig. 1). Impact Time Figure 1. Hypothetical impact of an invasive species on the invaded community over time. Overall impact rises at some rate during the establishment and spread phases, then the rate of increase of impact declines as the invader occupies all suitable habitat and areas. Impact reaches a plateau after which it either slowly declines, as previously hidden effects of adaptation and evolutionary compensation in the invaded community gradually reduce the effects, or continues to slowly increase if these compensatory changes are themselves considered to be components of impact. Impacts of invasive plants can be negative, positive or neutral, and in a particular invasion are typically composed of a mixture of such effects on different system components; so perceived impact on biodiversity is highly dependent on the measures of biodiversity that are assessed (Groves 2002). Effects can be identified at hierarchical levels from genetic, through individual to community and ecosystem, and can include extinction of other species, reduced abundance of native species and facilitation of other species. At one extreme, mere presence of an alien plant in a natural ecosystem may not be tolerated by humans (Groves 2002), even if the plant is accomodated in the system without other apparent negative effects. Transformer species Plants that cause major and permanent (or difficult to reverse) changes in invaded communities have been called “transformers” (Henderson 2001) or “ecosystem engineers” (Byers et al. 2002), although the latter term is usually applied to animals (Cox 2004). Transformer species often have a habit, life form or phenology not present in the invaded community (Woods 1997). Henderson (2001 p. 253) defined a transformer as a plant which can “as monospecies dominate or replace any canopy or subcanopy layer of a natural or semi-natural ecosystem, thereby altering its structure, integrity and functioning”. The definition is that of Swarbrick (1991), but not the terminology. Henderson (2001) contrasted ‘ruderal’ and ‘agrestal’ weeds, which “invade mainly sites of severe human disturbance”, with other invasive plant species – the implication being that invasion by transformers does not require such disturbance. Rather, such 18
species tend to be those which transform the system invaded by rapidly modifying the prevailing disturbance regime (Richardson and van Wilgen 2004). Transformer species often have disproportionately large effects compared to other weeds because they become numerically dominant in the invaded area or dominate the biomass. Good examples of transformer species are Mimosa pigra L. in Melaleuca woodlands in northern Australia (Braithwaite et al. 1989), Tradescantia in New Zealand forests (Kelly and Skipworth 1984) and Pinus and Acacia species in South Africa (Versfeld and van Wilgen 1986). Transformer grasses include ‘land builders’ such as Spartina (Gray et al. 1997), and Andropogon gayanus (Kunth) in northern Australia, which has massive stature in comparison to native grasses and greatly enhances the intensity and frequency of fires (Rossiter et al. 2003, Ferdinands et al. 2006). Impact of N. neesiana N. neesiana does not neatly fit the definition of transformer species in Australian native grasslands. It dominates the canopy in many invaded native grasslands, although its morphology, biomass and phenology is similar to some of the major native grasses that it replaces. The invaded systems remain as grasslands, and other effects it may cause are poorly known. The biodiversity impacts of N. neesiana in temperate Australian natural grasslands is probably critically determined by its presence and impact in the cultural steppe that surrounds and fragments the remaining indigenous remnants. The success of N. neesiana in the cultural steppe drives propagule pressure, so determines, in part, the susceptibility of grassland remnants to invasion. Their invasibility is also strong influenced by their health or degradation state, which is critically influenced by management. The prevalence of major anthropogenic disturbance and the disruption of ‘natural’ disturbance patterns appear to be central issues. A range of other factors most likely contribute to the success of N. neesiana in native grasslands and its biodiversity impact, including release from natural enemies. 19
Page 1 and 2: Literature review: Impact of Chilea
Page 3 and 4: Fire 49 Other disturbances 50 Shade
Page 5 and 6: Conventions and standards Botanical
Page 7 and 8: neesiana appears to be a habitat ge
Page 9 and 10: population densities of existing sp
Page 11 and 12: elated plants have similar defences
Page 13 and 14: For invasion to occur there must be
Page 15 and 16: As yet there appears to be no evide
Page 17: experimental manipulation of specie
Page 21 and 22: Taxonomy and nomenclature Stipeae N
Page 23 and 24: Vernacular names ‘Needlegrass’
Page 25 and 26: to Bouchenak-Khelladi et al. 2009).
Page 27 and 28: 1 m (Walsh 1994), ca. 90 cm (Verloo
Page 29 and 30: Figure 2. Anatomy of the seed of N.
Page 31 and 32: are the seeds larger/smaller, longe
Page 33 and 34: also based on a misunderstanding of
Page 35 and 36: Table 2. Modified Feekes Scale for
Page 37 and 38: Argentina, in the provinces of Chac
Page 39 and 40: Figure 3. Recorded distribution of
Page 41 and 42: 1994). Only 3 of 186 exotic grasses
Page 43 and 44: According to Morfe et al. (2003) th
Page 45 and 46: populations have been found in the
Page 47 and 48: (Honaine et al. 2006). The flechill
Page 49 and 50: In Australia the altitudinal range
Page 51 and 52: Proximity to urban development appe
Page 53 and 54: In the southern Brazilian campos of
Page 55 and 56: arundinacea (Gardener et al. 2005).
Page 57 and 58: al. 2008). Cues for masting may be
Page 59 and 60: Approximately 200 alien grass speci
Page 61 and 62: Dispersal of seed in contaminated s
Page 63 and 64: In New Zealand, Hurrell et al. (199
Page 65 and 66: No emergence was observed in undist
Page 67 and 68: and high impact (“ability to caus
Page 69 and 70:
also noted that despite a wide rang
Page 71 and 72:
a small reduction in seedhead produ
Page 73 and 74:
Slashing and mowing Slashing can re
Page 75 and 76:
Themeda re-establishment McDougall
Page 77 and 78:
species (Lawton and Schroder 1977 p
Page 79 and 80:
y increased importance of ant grani
Page 81 and 82:
BIODIVERSITY “Biodiversity ... on
Page 83 and 84:
According to Woods (1997 p. 61) “
Page 85 and 86:
2004, Richardson and van Wilgen 200
Page 87 and 88:
negative depending on the particula
Page 89 and 90:
Competition with native plants Comp
Page 91 and 92:
asexual seed production, so local f
Page 93 and 94:
GRASSLANDS Grasses: “... the most
Page 95 and 96:
susceptible to N. neesiana invasion
Page 97 and 98:
Floristic composition, vegetation s
Page 99 and 100:
proportion of the flora then presen
Page 101 and 102:
tussock space (Stuwe and Parsons 19
Page 103 and 104:
Like vascular plant diversity, comm
Page 105 and 106:
Opinions differ on the nature and i
Page 107 and 108:
Species Common Name Family Aust ACT
Page 109 and 110:
in shifting the distribution, exten
Page 111 and 112:
of these systems is largely explain
Page 113 and 114:
pasture. The least understood trans
Page 115 and 116:
tend to benefit more from relaxed c
Page 117 and 118:
Bovids crop their food between the
Page 119 and 120:
are therefore less likely to distur
Page 121 and 122:
esult in a “short-term flush” o
Page 123 and 124:
Fire effects on weeds Moore (1993 p
Page 125 and 126:
Table 8. Typical nutrient levels in
Page 127 and 128:
grasses produced sigificantly more
Page 129 and 130:
Fossorial vertebrates are or were o
Page 131 and 132:
(Rosengren 1999). Approximately one
Page 133 and 134:
Table 12. Areal extent and conserva
Page 135 and 136:
Foreman (1997) investigated the eff
Page 137 and 138:
Willis (1964) considered that the f
Page 139 and 140:
Austrostipa-Enneapogon) from around
Page 141 and 142:
Woodlands and New England Grassy Wo
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Thylogale billardierii), Peramelida
Page 145 and 146:
Its original habitat on the mainlan
Page 147 and 148:
Table 17. Endangered reptile specie
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equirement, but unlike plants and v
Page 151 and 152:
e assigned the same biodiversity sc
Page 153 and 154:
Nematodes are mostly minute animals
Page 155 and 156:
found in all mainland states, O. co
Page 157 and 158:
Keyacris scurra, Melbourne (1993) o
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was once widespread in south- easte
Page 161 and 162:
eing sluggish and wingless, and exi
Page 163 and 164:
estoration and, if Australia follow
Page 165 and 166:
close to the plant are able to bury
Page 167 and 168:
Species *Chirothrips mexicanus Craw
Page 169 and 170:
Table A2.1 (continued) Species Life
Page 171 and 172:
Table A2.1 (continued) Species *Het
Page 173 and 174:
Page 175 and 176:
Page 177 and 178:
Nematodes of grasses and grasslands
Page 179 and 180:
REFERENCES Aceñolaza, F.G. (2004)
Page 181 and 182:
Benson, D. and McDougall, L. (2005)
Page 183 and 184:
Chan, C.W. (1980) Natural grassland
Page 185 and 186:
DNRE (Department of Natural Resourc
Page 187 and 188:
Fuhrer, B. (1993) A Field Companion
Page 189 and 190:
Groves, R.H. and Whalley, R.D.B. (2
Page 191 and 192:
Iaconis, L. (2004) Chilean needle g
Page 193 and 194:
Levine, J.M., Adler, P.B. and Yelen
Page 195 and 196:
McDougall, K.L. (1987) Sites of Bot
Page 197 and 198:
Morfe, T.A., McLaren, D.A. and Weis
Page 199 and 200:
Perelman, S.B., León, R.J.C. and O
Page 201 and 202:
Saunders, D.A. (1999) Biodiversity
Page 203 and 204:
Thellung, A. (1912) La flore advent
Page 205 and 206:
Weiss, J. and McLaren, D. (2002) Vi
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